| Abstract
| - Excited state 7-hydroxy-4-methyl coumarin (4CUOH) has dual photochemical properties. In water, its neutralform (ROH*) is a strong photoacid and transfers a proton to the solvent with pK* ∼ 0. It is also a strongphotobase capable of accepting a proton from some protic solvents or reacting with excess protons in solution.In this study, we measured the rate and dynamics of the reaction of excited state 4CUOH with excess protonsin neat monols and water−glycerol solutions. The reaction shows diffusion-controlled reactivity and fits theSmoluchowski model. The reaction can be formulated by the kinetic scheme ROH* + H+ → RO*, whereRO* and ROH* are the protonated and neutral forms of the photobase, respectively. Nonexponentialdecay of the ROH* fluorescence was observed. We analyzed the experimental data within the framework ofthe diffusive model. The model predicts that the survival probability depends strongly on both the intrinsicrate constant and the mutual diffusion constant.
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